:confused:
Here is the scenario: Intermittently (every few weeks, sometimes more frequently, sometimes less) while highway driving 65-70 mph, start to feel slight vibration in steering wheel. It progressively gets worse, and after about 3 or 4 minutes, the steering wheel is literally shaking so badly that I have to pull off the road and stop the car. This is not an easy task, as when I brake, the shaking feels worse and it almost seems as if the car will not stop. Once it stops, it is OK for the remainder of the ride home. Once I believe I smelled a burning smell. My husband seems to think it is a caliper sticking. It has been back to the dealer (two different ones in fact) several times and since it is so intermittent, and they have not been able to duplicate the problem, they can do nothing for me they say. The rotors have already warped twice and been replaced. They say if it were a sticking caliper, the rotor would have been blue, which it was not. Any ideas? This is a potentially very dangerous situation as I can't always get to the right lane to pull off the road, and the car is difficult to control with the steering wheel shaking in my hands! It has happened about 9 or 10 times since I have owned the car (which is only about 18 months

change tires?

The most likely problem (IMO) is you have a defective tire. Once you drive and heat it up, a belt shifts and causes what you feel.

If your tires are old, replace them. If they have alot of tread left on them, ask your husband to bring the car to whoever sold you the tires and see if they can find something wrong with the tires (assuming they are reputable). If you don't trust them, have him bring it to another mechanic who deals in tires and have him look at it. If he can't find anything wrong with the tire, ask him to check the tie rods, ball joints, wheel bearings, lug nuts, etc. to see if anything is loose. If there is no problem with the front-end components, then replace the tires.

I doubt it is your brakes because the brakes sticking would make the car pull strongly in one direction, not make if vibrate.

I mentioned your husband because women do not generally get the quality of service from mechanics that men do.

Also, since you didn't say otherwise, I assume it is a used car. If it is new or under some sort of warranty, don't let the dealer off the hook. Keep bringing it back until they fix it. It sounds dangerous and shouldn't be driven at highway speeds until the problem is solved. Get it fixed.

May be a tire out of balance. A wheel weight could have fallen off. Also may be bad struts in front. One question, by any chance did you use fix-a-flat or any other type of quick tire repair? These inject miosture into the tire and throw off the balance. Like was previously stated, a good tire guy will find the problem.

I may be wrong, but in general, an out-of-balance tire will vibrate all the time you are going fast enough, not just intermittently.

True, but it may only be obvious or noticeable at higher speeds and/or certain road conditions. The same can be said for bad struts and shocks.
Moisture in a tire, whether from fix-a-flat or from air hoses which don't have driers, can throw off the balance. What happens is it accumulates in one area throwing the tire off. You hit a bump and the moisture gets dispersed and the tire temporarily regains some balance til it all accumulates again. I have seen moisture in tires many times.

Worth checking

I have a 2002 XLE v4 and I have experienced shaking in my steering wheel when braking at higher speeds. The problem for me was a warped rotor which is due to a bad design for 2002. The fix is to either get midas lifetime rotors or have the dealer install the newly designed rotors.